random access-range without lower-power range kinds?

[Lars T. Kyllingstad]

On Tue, 14 Dec 2010 09:09:33 +0100, spir wrote:

> Hello,
> 
> It seems impossible to define a random-access range (opIndex + length)
> alone. In fact, I cannot have it used by the language. Am I missing
> something? Random-access looks enough to provide fonctionality for both
> input and bidirectional ranges without any additional method. "Lowering"
> for forward iteration means I guess ;-)
> 	for (uint i=0 ; i < coll.length ; i++) {
> 	    element = coll[i];
> 	    doSomethingWith(element);
> 	}
> What is the reason for requiring methods of lower-power range types to
> be defined? (This makes 5 methods!)
> 
> Denis
> -- -- -- -- -- -- --
> vit esse estrany ☣
> 
> spir.wikidot.com


To avoid the boilerplate, you could write a mixin that defines the 
iteration primitives for you.

  mixin template IterationFuncs()
  {
      int index;
      bool empty() { return index == length; }
      auto front() { return opIndex(index); }
      void popFront() { ++index; }
      // ... etc.
  }

Then you'd just have to define opIndex() and length(), and the mixin does 
the rest for you.

  struct MyRange(T)
  {
      T opIndex(int i) { ... }
      @property int length() { ... }
      mixin IterationFuncs!();
  }

(I haven't tested the code above, so it probably has bugs, but you get 
the point.)

-Lars